Organic Contamination
Organic solids or semisolids are one of the
particulate contaminants found in hydraulic systems.
They are produced by wear, oxidation, or poly-
merization (a chemical reaction). Organic solid contami-
nants found in the systems include minute particles of
O-rings, seals, gaskets, and hoses. These contami-
nants are produced by wear or chemical reaction.
Oxidation of hydraulic fluids increases with
pressure and temperature. Antioxidants are blended
into hydraulic fluids to minimize such oxidation.
Oxidation products appear as organic acids,
asphaltics, gums, and varnishes. These products
combine with particles in the hydraulic fluid to form
sludge. Some oxidation products are oil soluble and
cause an increase in hydraulic fluid viscosity, while
other oxidation products are not oil soluble and form
sediment. Oil oxidation products are not abrasive.
Table 4-1.—Particle Contamination Level By Class
PARTICLE CONTAMINATION LEVEL—BY CLASS
MICRON
SIZE
RANGE
Acceptable
Unacceptable
0
1
2
3
4
5
6
5-10
2,700
4,600
9,700
24,000
32,000
87,000
128,000
10-25
670
1,340
2,680
5,360
10,700
21,400
42,000
25-50
93
210
380
780
1,510
3,130
6,500
50-100
16
28
56
110
225
430
1,000
Over 100
1
3
5
11
21
41
92
Total
3,480
6,181
12,821
30,261
44,456
112,001
177,592
NOTES
1. The class of contamination is based upon the total number of particles in any size range
per 100 ml of hydraulic fluid. Exceeding the allowable particle count in any one or more
size ranges requires that the next higher class level be assigned.
2. Class 5 is the maximum acceptable contamination level for hydraulic systems in naval aircraft.
Fluid delivered by SE to equipment under test or being serviced must be Class 3, or cleaner.
3. The Class 5 level of acceptability shall be met at the inspection interval specified for the
equipment under test.
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